Color motion picture film is a relatively recent development. Before the advent of color film stock in the 1950s, a process for making color motion pictures included capturing color information on two or more reels of black and white film. In the original Technicolor three-color film separation process, three reels of black and white film were loaded into a specially-designed movie camera. The light coming through the lens was split into the three primary colors of light and each was recorded on a separate reel of black and white film. After developing the three reels, three photographic negatives were created representing the yellow (inverted blue), the cyan (inverted red), and the magenta (inverted green) portions of the original scenes.
In addition to the creation of color separations through the original Technicolor process, color separations also have been produced and used for the archival of color film because black and white film stock generally has a much greater shelf-life than color film. In this process, the color film stock is used to expose one reel of black and white film with sequential records of red, green, and blue so that each frame is printed three times on the resultant reel to form a sequential separation.
Film studios may recombine the three color separations onto a single reel of color film using a photographic process that is performed in a film laboratory. In the case of three color separations that are each located on a separate reel, an optical film printer is employed to resize and reposition each source reel, one at a time. In particular, three passes are made. First, the magenta source reel is projected through an appropriate color filter onto the destination reel. Thereafter, the destination reel is rewound, the next source reel is loaded and resized, and the color filter is changed. The process is repeated until all three color separations have been printed on the single destination reel using the optical film printer. The resulting destination reel is called an interpositive (“IP”), and the colors are now represented as red, green, and blue (as opposed to cyan, magenta, and yellow).
The Technicolor three-color film separation process, as well as other processes, is subject to a variety of film distortions, including, for example, differential resolution. Differential resolution may arise because, for example, the nature of the light path and lens coatings in the Technicolor cameras typically cause the three film separations to have drastically different resolution or sharpness. The cyan filter typically is located behind the yellow filter in what is known as a bipack arrangement. Light that passes through the yellow filter is filtered and, unfortunately, diffused before striking the cyan filter. As a result, the yellow (inverted blue) separation typically has a greater resolution compared to the cyan (inverted red) separation. The magenta (inverted green) separation is not created with a bipack arrangement and typically has a resolution that is similar to that of the yellow (inverted blue) separation. This difference in resolution may result in red fringing or blurring around edges in the picture or image.